This invention relates to air cushioned landing systems for air vehicles, such as hybrid air vehicles.
The invention is particularly, but not exclusively, involved with the ground handling of hybrid air vehicles over rough or unprepared ground or water.
Hybrid air vehicles, as described in WO 2001/094172, are a form of airship that provide fuel efficient, long endurance freight transport/ISR capability through a combination of aerostatic lift, aerodynamic lift, and vectored thrust. Hybrid air vehicles tend to have bi-lobe or tri-lobe hulls extending longitudinally. This not only improves aerodynamic characteristics over traditional airships (single cigar-shaped hull) but also allows a wider base for improved ground handling.
The combination of aerodynamic lift and vectored thrust allows the vehicle to operate heavier-than-equilibrium, i.e. they are able to sit on the ground and use vectored thrust and aerodynamic lift to take-off. Vectored thrust also allows the vehicle to sit on the ground whilst lighter-than-equilibrium, i.e. the engine thrust pushes the vehicle on to the ground before ballast or payload is added to make the vehicle heavier-than-equilibrium.
Traditional airships require large numbers of ground crew to capture and launch the vehicle. They tend to be moored to a mast at roughly equilibrium with landing gear attached to the underside of the gondola and/or hull to absorb any movement.
Hybrid air vehicles can potentially dispense with large numbers of ground crew as they are able to land and take-off like conventional aircraft. Conventional aircraft landing gear could be used but this would limit the vehicle to operating from prepared sites.
Accordingly, a number of proposals have been made to provide airships and hybrid air vehicles with an Air Cushioned Landing System (ACLS). In particular, bag skirts have been proposed, for example formed toroidally, inflated with air and defining a central plenum in which air can be pressurised for use when landing or taxiing, or from which air can be evacuated to create suction to the ground when the air vehicle is lighter-than-equilibrium.
In some cases, the bag skirt can be deflated and is retractable during flight for better aerodynamics and possibly an improved field of vision for vehicle occupants and/or payload sensors. For example, WO 03/047967 describes bladder means attached to elongate bag skirts, retraction being effected by “zipping up” the bladder means. US 2012/0043416 A1 proposes bag skirt covers that unroll from extensible shafts to assist in retraction of the bag skirts.
The known retraction mechanisms are unreliable. They involve external moving parts, which may be elasticated or sprung, and are susceptible to jamming, snagging of ground debris, ice accumulation, etc.